This invention relates to means for cooling a valve adapted for use in an internal combustion engine.
Diesel engines, operating on high sulfur fuels, oftentimes contain vanadium compounds which require periodic "top end overhauls" or grinding of the exhaust valves due to corrosion effects and high heat levels imposed on the faces of the valves. Such corrosion tends to induce a "channelling" or "guttering" of the valve faces to accelerate such corrosion, thus giving rise to gas leakage past the valves and potential breakage of the valve heads. The corrosion effects also occur on the top of the valve heads which tends to induce severe pitting, also leading to valve head failures.
Metallurgical solutions have not fully solved the corrosion problem due to the high temperature levels experienced by the valve during operation thereof. Therefore, the state of the art has made various attempts to cool an exhaust valve by packing it with metallic sodium or other suitable cooling medium or by circulating oil through the valve. The former attempt, although exhibiting a desirable "cocktail shaker" action, has a tendency to raise the temperature level of the valve stem to thus reduce the service life of the tubular guide reciprocally mounting the valve in an engine. In particular, heat transfer necessary occurs by conduction through the valve stem, an oil film within the guide, the guide proper and the cylinder head boss surrounding the guide. As a consequence, the cooling medium contained in the valve will heat-up to an undesirable level to prevent efficient cooling of the valve face.
Also, circulation of oil through the valve for cooling purposes has not provided a final solution to the corrosion problem. In particular, a conventional valve arrangement of this type is primarily dependent on the principal of forced convection for cooling purposes, such as by the pumping of oil through a fill pipe and/or cavity. Thus, the cooling oil communicated to the head of the valve is not subjected to a desirable "cocktail shaker" action which would tend to provide for efficient distribution and flow of the cooling oil to the critical surface areas of the valve.
In addition, conventional multi-part valves of this type exhibit structural deficiencies which do not adequately counteract shear and bending stresses imposed on critical areas of the valve during operation thereof.